1. Field of the Invention
This invention relates generally to optically scanning and/or optically generating a pattern of figures such as arrays of image points, spots, or lines. More particularly, this invention relates to scanning and/or generating such patterns using a single rotating component that has sets of typically either two or three reflective surfaces that deflect an incident optical beam by various amounts.
2. Description of the Related Art
Optical scanners are a very mature technology and are most frequently represented by galvanometric scanners that oscillate a single mirror across an entry beam, or by a polygon scanner that has multiple reflective facets which are sequentially rotated through the entry beam. Galvanometric scanners have the disadvantage that they must be operated at low angular velocities to achieve constant displacement rates or to achieve a specific angular displacement pattern as may be required for micro-welding or medical treatment applications. Low duty cycle is another limitation of galvanometric mirror scanners because it takes substantial time to start and stop the galvanometer drive element for each point in the image array that must be addressed.
Polygon scanners operate at constant angular velocities, but they introduce a cross-scan random error associated with the machining errors on the individual facets and also due to run-out in the bearings that support the shaft of the polygon. This latter limitation is often mitigated by using expensive anamorphic relay optics to image the beam onto the facet in the cross-scan direction and more anamorphic relay optics to remove this one-dimensional power and form a round image spot. Another limitation of polygon scanners is the low duty cycle associated with a beam traversing a plurality of reflective facets.
For many optical pattern generators, the principal limitation is low duty cycle. The Broome optical pattern generator described in commonly owned, co-pending application Ser. No. 11/158,907, “Optical Pattern Generator Using A Single Rotating Component,” filed Dec. 29, 2005 by Barry G. Broome et al. is noteworthy for its improved duty cycle. The Broome optical pattern generator can reach duty cycles of 50% or better. In contrast, almost all prior art optical pattern generators used galvanometer mirror devices with duty cycles well below 50%.
Another limitation of most prior art optical pattern generators is that only linear patterns can be produced easily unless two independently-driven galvanometer mirror devices are used. In that case, synchronization of the two mirror devices is required and, due to the nature of galvanometer devices, it is still difficult to generate irregular two-dimensional patterns. Another limitation of most prior art optical pattern generators is that only narrow or collimated input beams can be used unless the duty cycle becomes very low.
Thus, there is a need for optical pattern generators with better capabilities than are currently available.